Parametric dependence of SAR on permittivity values in a man model

The development and widespread use of advanced three-dimensional digital an atomical models to calculate specific absorption rate (SAR) values in biolo gical material has resulted in the need to understand how model parameters (e.g., permittivity value) affect the predicted whole-body and localized SA R values. The application of the man dosimetry model requires that permitti vity values (dielectric value and conductivity) be allocated to the various tissues at all the frequencies to which the model will be exposed. In the 3-mm-resolution man model, the permittivity values for all 39 tissue -types were altered simultaneously for each orientation and applied frequen cy. In addition, permittivity values for muscle, fat, skin, and bone marrow were manipulated independently. The finite-difference time-domain code was used to predict localized and whole-body normalized SAR values. The model was processed in the far-field conditions at the resonant frequency (70 MHz ) and above (200,400,918, and 2060 MHz) for E orientation. In addition, oth er orientations (K, H) of the model to the incident fields were used where no substantial resonant frequency exists. Variability in permittivity value s did not substantially influence whole-body SAR values, while localized SA R values for individual tissues were substantially affected by these change s. Changes in permittivity had greatest effect on localized SAR values when they were low compare to the whole-body SAR value or when errors involved tissues that represent a substantial proportion of the body mass (i.e., mus cle). Furthermore, we establish the partial derivative of whole-body and localize d SAR values with respect to the dielectric value and conductivity for musc le independently. It was shown that uncertainties in dielectric value or co nductivity do not substantially influence normalized whole-body SAR. Detail ed investigation on localized SAR ratios showed that conductivity presents a more substantial factor in absorption of energy in tissues than dielectri c value for almost all applied exposure conditions.